As the feature size of device patterns get smaller for integrated circuits, the critical dimension (CD) specifications of these features become a more important criterion for stable and repeatable device performance. Allowable CD variation across a substrate processed within a processing chamber is difficult to achieve due to chamber asymmetries such as chamber and substrate temperature, flow conductance, and RF fields.
In processes utilizing an electrostatic chuck, uniformity of temperature control across the surface of the substrate is even more challenging due to the non-homogeneous construction of the chuck below the substrate. For example, some regions of the electrostatic chuck have gas holes, while other regions have lift pin holes that are laterally offset from the gas holes. Still other regions have chucking electrodes, while other regions have heater electrodes that are laterally offset from the chucking electrodes. Since the structure of the electrostatic chuck can vary both laterally and azimuthally, uniformity of heat transfer between the chuck and substrate is complicated and very difficult to obtain, resulting in local hot and cold spots across the chuck surface, which consequently result in non-uniformity of processing results along the surface of the substrate.
The lateral and azimuthal uniformity of heat transfer between the chuck and substrate is further complicated by heat transfer schemes commonly utilized in conventional substrate supports to which the electrostatic chuck is mounted. For example, conventional substrate supports typically have only edge to center temperature control. Local hot and cold spots within the electrostatic chuck cannot be compensated for while utilizing the heat transfer features of the conventional substrate supports.